This invention relates to a platen roller type recorder or printer/plotter in which a paper supply is frictionally driven by the platen and, more particularly, to such apparatus having a multiple roller cylindrical platen with the paper supply being driven by the center roller of the platen.
In the conventional platen roller type recorder or printer/plotter, a one-piece platen is utilized and the paper is either supplied thereto by parallel sprockets aligned with holes in the edges of the paper supply or the paper supply is driven by frictional contact with the platen. Sprocket drives, although providing an excellent paper feed and alignment require extra parts, must have the drive synchronized, and must have special paper with holes that mesh with the sprockets, all of which add to the complexity and expense of the equipment in which the recorder is utilized.
When the paper is frictionally driven by the platen, if the ends of the platen are not of exactly the same diameter--which is difficult to achieve with metallic platens and practically impossible to achieve with rubber--the larger end of the platen drives the paper faster than the smaller end. This results in skewing of the paper which gets progressively worse as more and more paper is fed to the platen. Also, in such frictional drive arrangements, the paper is usually held against the platen by at least two rollers which are located in the proximity of the ends of the platen. This compounds the problem because the paper is forced to be driven at different speeds by the different size ends of the platen with no chance to slip to accommodate the difference in size between the ends.
Another problem occurs when the paper supply is not fed perfectly square to the platen. When the paper is presented at an angle, it tends to spiral along the platen and ultimately is driven off the end thereof. Careful adjustment can align the paper and correct this problem but such adjustment is time-consuming and costly. Furthermore, repeated adjustments may be required during the operation of the recorder as, for example, in the use of a folded paper supply which has not been folded perfectly square, or when new supplies are required on the exhaustion of the paper supply.